Caption: Penguins mating, artwork. The penguins' reproductive organs are shown here, with the male on top and the female on the bottom. Like all birds, penguins have a cloaca, which is a combined intestinal, urinary and reproductive tract. The male has internal testes (oval, grey), with the larger left one seen here. Sperm is deposited in the female's cloaca. As eggs leave the female's single ovary (pink), they can be fertilised by this sperm. The fertilised egg is then laid by the female and incubated until hatching. The kidneys (red) are also shown here.